This invention relates to a shaft seal assembly for sealing a rotating shaft penetrating a pressure barrier and specifically to a traction drive shaft seal assembly for shafts rotating at high-speeds penetrating high-pressure barriers.
In many applications, a rotating shaft penetrates a pressure barrier to rotate a vane or rotor within a pressure chamber. A potential leak point is the interface between the shaft and the pressure barrier. Sealing the shaft/pressure barrier interface is typically accomplished by selecting suitable material for a mechanical contact seal between the rotating shaft and the pressure chamber housing. Selecting the proper material for each application is dependent on a known design parameter referred to as PV. The PV for a seal is determined by multiplying a seal contact pressure (P), by a surface velocity (V) of the shaft. The specific PV value for an application is then matched to known materials to construct a suitable shaft seal.
In typical applications, the pressure and velocity of the rotating shaft allows for use of common known materials for construction of the seal. However, there are extreme applications where shaft speeds may exceed 80,000 rpm and pressures may exceed 500 psi. In such extreme applications, the PV values are such that known materials are unsuitable to adequately seal the shaft pressure barrier interface within acceptable leakage limits.
Other types of seals such as Ferromagnetic seals are not suitable for such extreme shaft speed and pressure combinations. Further, a single spring loaded carbon face seal is not acceptable because the operating speeds of the shaft and pressure within the pressure chamber combine to require a PV value greater than 30 times allowable material combinations.
Accordingly, it is desirable to develop and design a seal that can use known materials for high speed, high-pressure applications while providing a relatively low leakage.